The present invention relates to a rotor balancing method and system for reducing the amplitude of excessive vibration occuring in a rotor system of a rotary machine.
In general, it is quite difficult to produce the rotor of a rotary machine in perfect symmetry around a longitudinal axis of the rotor. Accordingly, the rotor often has mass unbalance. As the rotor having such mass unbalance is rotated, the mass unbalance causes a centrifugal force to act on the rotor to cause an unbalance vibration to occur. The presence of considerable mass unbalance in the rotor causes an excessive vibration thereof and, the excessive vibration results in an abnormality of the bearings by which the rotor is rotatably supported thereby resulting in a failure of normal operation of the rotor.
It will be understood from the foregoing that, in the rotary machines having rotors, it is quite important to avoid any accident attributable to the rotor vibration, to thereby improve the reliability of the rotary machine and to ensure the satety thereof. From this point of view, it is a matter of great significance to accurately and efficiently perform the rotor balancing which is the technique for reducing the vibration amplitude.
Generally, the results of the rotor balancing are evaluated by whether the vibration amplitude has reduced below a predetermined allowable level. Hithereto, various rotor balancing techniques have been used depending on the type of the rotor and the speed range of operation of the rotor. Usually, however, the rotor balanicing is made by adding a correction mass to the rotor to reduce the vibration amplitude. The term "correction mass" is used here to mean a vector mass having concepts of angle and magnitude. More specifically, the "correction mass" is the vector mass defined as having a circumferential angular position to which a correction mass is to be added, and the correction mass. Therefore, in the conventional rotor balancing technique, it is a key for reducing the vibration amplitude to adequately select the correction mass, and to choose an optimum correction plane to which the mass is to be added, from a plurality of axially-spaced correction planes which exist lengthwise of the rotor. The selection of optimum correction mass and the optimum choice of the optimum correction plane are generally difficult and time-consuming and, accordingly, seriously hinders the quickness and accuracy of the rotor balancing.
The choice of the correction plane in the conventional rotor balancing largely relies upon the high experience and knowledge of the skilled operator, so that the choice takes an impractically long time to impose a serious problem from the view point of quickness of the operation. More specifically, the mass unbalance on the rotor is optionally distributed along the length of the rotor. In addition, in most cases, the correction plane to which the correction mass is to be added can take a plurality of positions extending lengthwise. In the conventional rotor balancing, however, the choice and determination of the correction plane have been made by skilled operators having good experience and knowledge, taking into account various factors such as vibration mode of rotor. Operators having good experience will be able to determine the optimum correction plane in a short period of time, if only few correction planes exist. However, if he is not experienced enough, he will have to determine the correction plane through a trial-and-error method taking a long time even if the number of conceivable correction planes is small. In the case where a plurality of correction planes exist along the length of the rotor and enormous data have to be taken into consideration for the reduction of vibration amplitude, as in the case of the rotor of a turbine generator, it is quite difficult to determine the optimum correction plane in a short time, not only for unskilled operators but also the operators who have abundant experience and knowledge.
U.S. Pat. No. 4,098,127 discloses a process for determining the correction mass to be added to the correction plane on the basis of enormous data. This process is effective only when the correction plane to which the mass is to be added is designated or given, and cannot apply at all to the determination of correction plane and correction amount in the case where a plurality of correction planes are conceivable.